Is a blood pressure of 140/100 deadly or dangerous??

Neither: Blood pressure greater than 140/90 on average (measured several times over several days) is defined as hypertension. Initial treatment is to avoid things that might elevate it such as alcohol and salt and to engage in active diet exercise and wt loss. Next step is to treat with medications. Some argue that over age 65 BP does not need to be treated unless >150/90.

Blood pressure: 140/100 is high blood pressure. It isn't deadly or dangerous as a one time phenomenon but left untreated, could be very problematic long term.